The achievement marked the first time U.S.-based airlines reported no such lengthy interruptions since the agency began to keep track of them in 2008. The agency reported 11 delays lasting longer than three hours in October 2009.

Passenger rights advocates attribute the accomplishment to new penalties adopted by the Department of Transportation. Beginning in April, airlines that strand passengers on planes for more than three hours without allowing them to return to the gate can be fined up to $27,500 per passenger.

While the Department of Transportation continues to investigate several delayed flights, it has yet to issue a fine under the new rules.

"The reality of the rule is that it has made the airlines do the right thing and made travel better and more humane for everyone," said Kate Hanni, founder of flyersrights.org. "It's proof that protecting passengers can be both efficient and good business."

Hanni, who become a vocal airline critic since she and her family were stuck on a plane for nine hours on a tarmac in Austin, Texas, in 2006, was among many who pushed for the fines last year.

Most major airlines opposed the fines, saying they would prompt carriers to cancel flights to avoid paying the penalties.

The federal agency reported that there were only 12 tarmac delays of more than three hours reported from May through October, compared with 546 during the same five-month period in 2009.

The Department of Transportation also reported Tuesday that the nation's largest carriers canceled 0.97% of their scheduled domestic flights in October, down from the .99% cancellation rate of October 2009. They posted a .90% cancellation rate in September 2010.

-- Hugo Martin

Photo: An American Airlines flight takes off from Los Angeles International Airport. Credit: Los Angeles Times.